Process for hot-wet calendering fabrics



July 9, 1963 L. H. MESSINGER 3,096,557

PROCESS FOR HOT-WET CALENDERING FABRICS FIG.

Filed Jan. 3, 1961 2 Sheets-Sheet l FABRIC WET WITH WATER WET FABRIC HEATED UNDER PRESSURE PRESSURE RELEASED WATER IMMEDIATELY VAPORIZES INVENTOR LESTER HUBERT MESSENGER ATTORNEY y 1963 L. H. MESSINGER 3,096,557

PROCESS FOR HOT-WET CALENDERING FABRICS Filed Jan. 3, 1961 2 Sheets-Sheet 2 FIG.3

INVENTOR LESTER HUBERT M ESSINGER ATTORNEY United States Patent 3,096,557 PROCESS FOR HOT-WET CALENDERING FABRICS Lester Hubert Messinger, Newark, DeL, assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed Jan. 3, 1961, Ser. No. 80,052 12 Claims. (Cl. 26-1) This invention relates to a process for the improvement of fabrics constructed of a synthetic filamentary material, and more particularly to a process for improving the cover and reducing the slickness of fabrics containing synthetic filament yarns.

Fabrics woven and knitted from continuous filament yarns of the synthetic fiber group are deficient in fabric aesthetics in that they possess a smooth sheen, do not cover well, and the smooth, close contact with the skin makes them feel hot and clarnmy in summer and cold in winter. These fabrics possess properties which are distinctly different from fabrics made of spun yarns from synthetic staple fibers, which possess loose ends on the short fibers and reduce the effect of the three above mentioned objections when used in wearing apparel. However, even fabrics of spun synthetic yarns are somewhat deficient in comfort and cover.

It is an object of this invention to provide a process for improving the aesthetics of apparal fabrics constructed of continuous filament yarns or spun yarns of synthetic filamentary materials. Another object is to remove the sheen from said fabrics, increase the fabric cover, and reduce the fabric slickness by providing a multiplicity of extended protrusions on the surface of the individual fibers and filaments. Other objects will become apparent as the description of the invention proceeds.

These objects are accomplished by the present invention which provides a process for improving the aesthetics of a fabric containing a preponderance of filaments composed of a synthetic, high-melting, fiber-forming polymer which comprises passing the fabric, which is wet with water, through two confining structures, heating the fabric and water to a temperature of from 200 to F. below the softening point of the said synthetic polymer while maintaining at least sufficient pressure between the confining structures to maintain the fabric in the wet condition as it passes through said structures, and thereafter immediately releasing the pressure from the fabric.

The term preponderance is used to signify that the fabric is composed of more than 50% (on a weight basis) of filaments formed from the synthetic polymer. By synthetic, high-melting, fiber-forming polymer is meant a man-made, non-cellulosic polymer having a melting point above about 250 F. which is suitable for the formation of textile fibers. Many such suitable materials are included within the descriptions of United States Patent Nos. 2,190,770; 2,130,948; 2,667,468; 2,465,319; and 2,511,544. The term confining structures is used to mean structures which hold and confine the fabric (as well as the Water in the fabric) under sufficient pressure that the water is held within the fabric until the release of the pressure. Thus, even though the water is heated to a temperature about its boiling point, it is still confined within the fabric until the pressure is released. Upon the release of pressure, however, the water immediately vaporizcs and leaves the fabric in all directions.

The invention will be more readily understood by reference to the drawings.

FIGURE 1 is a diagrammatic flow sheet of the process of the present invention.

FIGURE 2 is a draftsrnans conception of a photomicrograph of a fabric of the invention. In FIGURE 2, the extended protrusions are shown as small tapered pro- 3,096,557 Patented July 9, 1963 "ice trusions on the fabric surface. In other instances, the protrusions appear to be more in the form of scales projected outwardly from the surface rather than hair-like as shown in the figure.

FIGURE 3 is a schematic representation of an embodiment of the process of the invention. In FIGURE 3 wet fabric 1 is passed between confining rollers 2 and 3, roller 2 being a hard, rough-surfaced, hot roller and roller 3 being an unheated compressible roller. As the fabric leaves the nip of the rollers, its water content is substantially reduced.

In a preferred embodiment of the present invention, the fabric, consisting essentially of continuous filaments, is wet with water, is passed, at a speed of from about 15 to about 35 yards per minute, between the two confining rollers of a conventional calender machine which exert a pressure on the fabric of from about 500 to about 2000 pounds per inch of roll width; one of the said rollers being a hard, roughsurfaced roller heated to a temperature of from 200 to 10 F. below the softening point of the said synthetic polymer of the fabric and the other roller being an unheated compressible roller. In such a case, the pressure on the fabric is immediately released as the fabric emerges from the rollers, and the protrusions produced appear on the face of the fabric adjacent the heated roller.

It is essential that the fabric be wet prior to and during the compression through which it is led since a dry sheet or fabric of the composition of this invention, when passed between compressing structures and heated, would not exhibit the desired properties of this invention but would appear as a glazed parchment-like sheet or fabric. It is preferred that the sheet or fabric be wet with at least about 20% by weight water, based on the total weight of dry fabric to produce the desired results; however, the water content of the fabric may be less than this amount. It should be understood that while the process of this invention may be accomplished with a water content in the fabric of less than the preferred amount, a much reduced water content will affect the desired results to a degree that as the water content of the fabric approaches zero the tendency to produce a parchmentlike glazed sheet increases.

After the release of pressure on the fabric, which allows the vaporization of the water, it may be subjected to hotwet mechanical working, e.g., sanforizing or fulling, and to heat treatment to further improve the physical properties. This, of course, is optional and would depend on the use to which the finished fabric would be put.

The following examples are cited to illustrate the invention and are not intended to limit it in any manner.

Example I A taffeta fabric of loom count 104 ends X 76 picks is woven from 70 denier, 34 filaments of semidull poly (ethylene terephthalate) continuous filament yarn. Water at to 200 F. is padded on the 42-inch wide fabric. Approximately 12 inches from the padding roll the fabric continuously passes over two stationary steel rolls and then moves another 12 inches to the top of the two calender rolls, each 48 inches in width. One roll is a steel Schreiner calender having 260 lines per inch and the compressible roll has a composition surface made of a mixture of cotton and corn husks. Excess water (which is heated near the boiling point) wrings from the fabric at the nip. Excellent results are obtained with the surface temperature at the nip of the heated Schreiner roll at 440-460 F. The roll pressure is 1666 pounds per inch of roll width (i.e., 40 tons) and the roll speed 20 yards per minute. Immediately after emerging from the nip of the rolls the fabric is quite stiff and boardy. It is then subjected to vigorous mechanical action While scouring at 190 to 210 F, heat set under slight extension in both warp and filling directions at 400 F. for 30 seconds, and then subjected to the action of a 3% aqueous solution of sodium hydroxide at 212 F. until it loses 12% by weight. The fabric is then rinsed and dried. The fabric has a desirable subdued luster, a greatly improved covering power, and a must softer and less slick surface, compared with the original untreated fabric. Microscopic examination of individual filaments taken from the fabric surface show that a profound change in surface characteristics has occurred. Each filament has numerous protrusions of a scaly nature.

Example II Two plain-weave blended fabrics are prepared, one made from a blend of 45% cotton and 55% 3-denier poly(ethylene terephthalate) staple fiber having a staple length of 2.5 inche and the other being made from 85% poly(ethylene terephthalate) staple fiber and 15% rayon staple fiber, both having a denier of 3 and a staple length of 3 inches. Each of the two fabrics are processed under exactly the same conditions as those described in Example I except that a different heated roll is used and the treatment with sodium hydroxide is omitted. Substantially the same results are obtained as those set forth in Example I.

Example III A satin fabric is woven from 70 denier, 34 filaments of bright poly(hexamethylene adipamide) continuous filament yarn using a 1 x 4 twill weave, and loom count of 110 ends x 81 picks. This fabric is processed under exactly the same conditions as those described in Example Il, except that the surface temperature of the heated roll is dropped to 400 to 410 F. The fabric is characterized by a pleasant subdued luster, a greatly increased covering or hiding power, good drapability, and a soft, almost suede-like, surface hand. Microscopic examination of individual filaments dissected from the fabric surface shows them to have numerous protrusions of a \airy nature.

Example IV A tricot fabric is knitted by feeding dull continuous filament poly(hexamethylene adipamide) yarns (40 denier, l3 filaments with /2 Z twist) to both bars of the knitting machine, using 85 wales X 90 courses construction. This fabric is processed under exactly the same conditions as those described in Example 11, except that the heated roll temperature is 400 to 410 F. and, prior to heat setting, the fabric is subjected to rather severe temporary widthwise stretching to break up temporary bind points between and within the yarns. These tend to make the fabric excessively stiff and harsh unless the temporary stretching operation is applied. The fine hairlike projections on the surface of this fabric increase the friction considerably, so that it is better suited to use as bed sheeting than an uncalendered control fabric. The improvement in friction is demonstrated by positioning fabric samples on an inclined plane surface at a 45 angle and then placing a disc covered with woolen blanket material on the fabric-covered inclined plane. When the fabric covering the inclined plane is the unmodified tricot control sample, the disc immediately slide down the inclined plane. However, when the fabric covering the inclined plane is the tricot sample processed according to this invention, the blanket-covered disc does not slide down the inclined plane even when the angle is increased to 60. In addition to improved frictional properties, the tricot fabric wet calendered in accordance with this example has greatly improved covering and hiding power. Thus, while the light transmission of an untreated control fabric is 18.6% under standard test conditions, that of the wet calendered fabric of this example is only 5.2%.

4 Exmnple V A fabric consisting of 65% by weight 1.5 denier per filament, 1% inch staple fiber of ethylene terephthalate polymer blended with 35% 1.5 denier per filament, 13th; inch staple rayon and containing 40/1 cc. (cotton count) warp yarns and 45/1 cc. filling yarns is woven in a plain weave with a ends x 74 picks per inch construction. This fabric is finished by singeing, desizing, scouring in open width, drying to 30% water content by weight of dry fabric, and then calendering at 390 F. and 25 yards per minute using a nip pressure of 0.5 ton per linear inch and a calender roll with a surface construction of 260 lines per inch oriented at 45 from the warp yarns. The finishing was continued by heat setting at 385 F. a 45 /2 inch width in a clip tenter, singeing, bleaching, tinting and sanforizing.

This fabric has cover equal to cotton broadcloth as measured by visible light transmission (2.8% vs. 3.0%), has luster equal to cotton broadcloth as shown by reflected light (70 vs. 79) and has more crispness than cotton broadcloth. The fabric finished as described above has superior cover and luster in comparison with a control fabric of ethylene terephthalate polymer/rayon, finished in the same manner except that the calendering step was omitted.

Example VI A worsted-type flannel fabric is prepared from a blend of 55%, 4.5 denier per filament poly(ethylene terephthalate) staple fiber and 45% wool and is woven in a 2 x 2 left-hand twill weave pattern at a loom construction of 69 ends x 67 picks using 16/1 cc.l4$ warp yarns and 16/1 cc.11Z fill yarns. This fabric is finished using a conventional procedure which includes scouring, napping, fulling, scouring, drying, heat setting, shearing, pressing and semi-decating. The finished fabric is then subjected to a hot-wet calendering treatment which consists of wetting it out to a 60% moisture content pickup and then passing it between a heated Schreiner roll (350 F.) and a composition roll (unheated) at 1000 pounds per inch linear pressure. The fabric is then given an after-scouring in a heck at F., dried and then repressed. The after-scouring treatment is deemed necessary to remove excess fabric stiffness developed during calendering. Presumably, the wool absorbing moisture swelled the yarn bundles and under the influence of the mechanical working in the beck broke up the compacted structure.

The resultant fabric is found to have more worstedlike luster than an uncalendered sample along with a more felt-like surface cover similar to that which is developed in finishing 100% Worsted flannels. This is a permanent effect since the improved cover and luster persisted through 600 hours of actual wear testing. Examination of the structure before and after calendering reveals that the rod-like poly(ethylene terephthalate) fibers have developed a very fine micro-crimp along their longitudinal axis which apparently oriented light reflectance to give an illusion of a felt-like surface and higher degrees of luster. There are no indications of ruptured fiber surface such as is exhibited in the hot-wet calendering treatment on nylon tricot structures.

The present process is based on a critical selection of processing variables which must be controlled simultaneously in order to achieve the improved fabrics which are the object of this invention. The temperature of the heated rough-surfaced roll at the nip should be maintained at 200 to 10 F. below the softening point of the filamentary material used in the particular fabric being processed. This temperature will vary, depending upon the softening point of the fibers and filaments. For example, for polyamide fabrics the preferred hot roll temperature at the nip is 360 to 410 F., depending upon the fabric thickness. For fabrics constructed of acrylic polymer and copolymer filaments, the preferred hot roll temperature is 275 to 325 F. For fabrics constructed of polyester yarns, the preferred hot roll temperature is 325 to 475 F. The roll pressure at the nip should be such that enough hot water is retained in the nip to keep the fabric just wet-out during its passage through the nip. A satisfactory operating range of pressure is 500 to 2000 pounds per inch of roll width.

The speed of the two calender rolls carrying the fabric must be sufiiciently high that the water enters the nip with the fabric before it can be heated to boiling temperature and flashed olf. On the other hand, the speed must be sufficiently low to permit water in the nip to reach the necessary temperature depending upon the fabric type used. A satisfactory operating range of peripheral roll speed is to 35 yards per minute for most fabrics.

Normally the temperature of the wet fabric must be raised and maintained close to the boiling point of water just before entry into the nip in order to avoid cooling the roll excessively, and yet the fabric must not be too hot or the water will flash from the fabric prematurely. It is certainly possible to start with a water temperature which is even cool or cold, but it is far more practical to have the water temperature in the desired range in the first instance since, if this is not so, time and energy must be expended during the process to obtain the desired water temperature.

One of the calender rolls is normally made with a rough hard incompressible surface which allows the fabric to be compressed slightly below the surface of the roll in a number of points across the surface. This is the heated hard-surfaced roll and its surface may be made of alloy steel, plastic, ceramic or coated metal such as chromium or nickel plated steel. The surface is preferably rust resistant. The second roll is made of a compressible composition, such as cotton, paper, wool, corn husk or other material that will present a tough resilient unpattcrned surface to the fabric when compressed against the first roll. The action of the second roll is to seal the water within the nip and prevent expansion into steam before the water has been heated to or near the temperature of the hot roll.

It was mentioned earlier that the fabric must be Wet prior to compression. The preferred working range is from about to 60% wet by water based on total dry weight of the fabric. composed of more than 50% of filaments formed from synthetic polymer by the method of this invention would produce a parchment-like sheet having a glazed surface. The surface of the synthetic filaments is plasticized only in the presence of sufficient water. It is only in the presence of sufficient moisture that the surface of the synthetic filaments can be modified to produce the scaly or hairlike protrusions by the process of this invention and thus obtain the desirable physical properties. A desirable amount of moisture would be at least about 20% by weight water based on the total dry Weight of the fabric; however, this is not to say that the process will not work with a lesser amount. It must be understood, however, that while the process would work, the resultant fabric would exhibit the desired properties to a lesser degree as water content was reduced much below the preferred 20% and that at a point near the zero water content, the desirable properties of this invention would not appear in a fabric otherwise processed as taught herein.

While the scope of this invention is not to be limited by any particular theory, it is believed the critical conditions specified for calendering the fabrics cause numerous fine hair-like protrusions to be forced or drawn out of the individual filaments and fibers of a yarn without changing their external appearance. These protrusions are usually a fraction of the diameter of the filament itself and several times longer than the filament diameter. Their formation might be explained by the theory that moisture within the filament is heated under high pressure to a point approaching the flash temperature at that Processing a dry sheet of fabric pressure. When the pressure is released, the moisture flashes into steam and pulls some of the polymer from the inside of the filament as it escapes. Through the microscope, it can be seen that any hairs which are unobstructed shoot straight out of the filament, but those that exit within the yarn bunch up and force the filaments apart. This action upsets the symmetry of the yarn and results in increased fuzz or nap on the fabric, causing increased cover and decreased sheen. The volurne of the filaments, yarns and fabric is increased; hence the fabric thickness is not decreased as is the case in conventional calendering of fabrics which flattens the yarn bundles. The critical processing conditions of this invention force hot water into the fabric structure and hold this water within the fabric in the liquid state under pressure until the water at the nip reaches the temperature of the surface of the heated roll. Then the pressure at the nip is instantaneously released, allowing superheated Water to flash into steam and, by this action, to disrupt the smooth surface of individual filaments and fibers which have absorbed water. This essential action of disrupting the surface of the filamentary material is carefully timed and controlled to take place substantially entirely and immediately after the release of constraint rather than during the period of constraint.

It should be obvious that in the wetting treatment to which the fabric is subjected, minor amounts of wetting and other like agents may be present to facilitate contact with the water without impairing the process of this invention.

The chief advantage of the present invention is that it provides a process for producing fabrics containing a preponderant amount of man-made filamentary material similar in properties to fabrics constructed of conventional man-made spun yarns, with the added advantage that the fabrics of this invention contain many more minute surface fibers 0r hairs, and each hair is much finer and softer than the conventional loose ends found in spun yarns. Hence, the calendered filament fabrics resulting from the present invention possess much im' proved friction qualities, especially polyamide tricot knit fabrics, than do conventional man-made spun fabrics. A further advantage is that the present invention provides a process for reducing and even removing sheen from fabrics constructed of man-made filament and spun yarns, including blends of man-made yarns with cellulosic and/ or natural yarns, increasing the cover of said fabrics, and reducing the slickness of said fabrics.

The process of the present invention may be applied to any woven, knitted, or non-woven fabrics constructed from a preponderant amount of man-made filamentary material. The term filamentary material as used herein refers to either staple fibers or continuous filaments employed in making the fabrics. Typical examples of manmade fibers and filaments include those prepared from polyamides such as poly(h-examethylene adipamide), poly(hexamethylene sebacamide), polycaproamide, and copolyamides, polyesters and copolyesters such as condensation products of ethylene glycol with terep-hthalic acid, ethylene glycol with a 90/10 mixture of. terephthalic/isophthalic acids, ethylene glycol with a 98/2 mixture of terephthalic/S-(sodium sulfo)-isophthalic acids, and trans-p-hexahydro-xylylene glycol with terephthalic acid, polyacrylonitrile, copolymers of acrylonitrile with other monomers such as methyl acrylate or vinyl pyridine, vinyl and vinylidene polymers and copolymers, polycarbonates, polyurethanes, polyesteramides, polyethylenes, polypropylenes, fluorinated ethylene polymers and copolymers, and the like.

Considerable improvement in hand and cover also may be obtained when blends of man-made filamentary material with up to by weight of cellulosic and/or natural fibers and filaments, such as cellulose acetate, cellulose triacetate, viscose rayon, cotton, wool and the like, are processed in accordance with this invention. A shirt, blouse, dress, or similar garment can be made which will have an acceptable appearance and can be worn without ironing after receiving a complete automatic machine-wash, tumble-dry home laundry cycle. For best results, the garments should be tumbledried at 158:43 F. The garment can be made of a fabric containing an intimate blend in both warp and filling of at least 55% poly(ethylene terephthalate) fiber with viscose rayon as the remainder of the blend. Typical fabric constructions which will give the required performance are batistes, broadcloths, and oxfords. To have acceptable seam appearance after the machine-wash and tumbledry cycle, low thread tensions during sewing are required. As an example, tension in the range of 150 to 200 grams should be used on a lock-stitch machine. In addition, it may be necessary to utilize special threads or special seaming devices to obtain the best seam appearance. As an example, a bobbin thread which elongates to 15% on heating to 320 F. can be used to give the required seam appearance after the automatic wash-tumble-dry cycle.

Specific fabric types which are greatly improved with regard to aesthetics and comfort include tricot fabrics, woven undergarments, bed sheeting, pillow cases, shirtings, blouse and dress fabrics, and other apparel and industrial fabrics.

Many other equivalent modifications will be apparent to those skilled in the art from a reading of the foregoing without a departure from the inventive concept.

This application is a continuation-in-part of the United States application Serial No. 746,341, now abandoned, and U.S. application Serial No. 821,127 filed June 18, 1959.

What is claimed is:

1. A continuous process for improving the aesthetics of a fabric containing a preponderance of filaments composed of a synthetic, fiber-forming polymer having a melting point above about 250 F. which comprises passing the fabric, which is wet with water, at a speed of at least about 15 yards per minute, through two confining structures, heating the fabric and water to a temperature of from 200 to F. below the softening point of the said synthetic polymer while maintaining suffieient pressure between the confining structures to maintain the fabric in the wet condition as it passes through said structures and thereafter immediately releasing the pressure from the fabric to vaporize at least part of the water which leaves the fabric in all directions to form a multiplicity of extended protrusions on the surface of individual filaments in said fabric thereby improving the cover and reducing the slickness of the fabric.

2. A continuous process for improving the aesthetics of a fabric containing a preponderance of filaments composed of a synthetic fiber-forming polymer having a melting point above about 250 F., which comprises passing the fabric between confining structures at a speed of at least about yards per minute and confining the fabric, which is wet with at least by weight of water, based on the total dry weight of the said fabric, between said confining structures, heating to bring the fabric and water to a temperature of from 200 to 10 F. below the softening point of the said synthetic polymer while maintaining sufficient pressure between the confining structures to maintain the fabric in the wet condition and thereafter immediately releasing the pressure on the fabric to vaporize at least part of the water which leaves the fabric in all directions, to form a multiplicity of extended protrusions on the surface of individual filaments in said fabric thereby improving the cover and reducing the slickness of the fabric.

3. A continuous process for improving the aesthetics of a fabric containing a preponderance of filaments composed of a synthetic, fiber-forming polymer having a melting point above about 250 F. which comprises passing the fabric, which is wet with water, at a speed of from about 15 to about yards per minute, between two confining rollers which exert a pressure on the fabric of from about 500 to 2000 pounds per inch of roll width, one of the said rollers being a hard, rough-surfaced roller heated to a temperature of from 200 to 10 F. below the softening point of the said synthetic polymer of the fabric and the other roller being an unheated compressible roller, to heat the fabric and water therein while maintaining the fabric in wet condition as it passes through said rollers, immediately releasing the pressure on the fabric to vaporize at least part of the water therein which leaves the fabric in all directions, to form a multiplicity of extended protrusions on the surface of individual filaments in said fabric thereby improving the cover and reducing the slickness of the fabric.

4. The process of claim 2 wherein after releasing the pressure on the fabric, the said fabric is then subjected to hot-wet mechanical working followed by a heat-setting treatment.

5. The process of claim 2 wherein the fabric is composed of continuous filament yarns.

6. The process of claim 2 wherein the fabric is com posed of spun yarns.

7. The process of claim 2 wherein the fabric is knitted.

8. The process of claim 2 wherein the fabric is woven.

9. The process of claim 2 wherein the fabric contains both synthetic and natural staple fibers.

10. The process of claim 2 wherein the polymer is poly(hexamethylene adipamide) 11. The process of claim 2 wherein the polymer is poly( ethylene terephthalate) 12. The process of claim 2 wherein the fabric is nonwoven.

References Cited in the file of this patent UNITED STATES PATENTS 2,110,371 Radford Mar. 8, 1938 2,268,160 Miles Dec. 30, 1941 2,712,170 Phillips July 5, 1955 2,828,528 Gajjar Apr. 1, 1958 2,972,177 Bidgood Feb. 2], 1961 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,096,557 July 9. 1963 Lester Hubert, Messinger It is hereby certified that error appears in the above numbered patent reqiiring correction and that the said Letters Patent should read as corrected below- Column 1 line 27, for "apparel" read apparel column 3, line 8, for "must" read much column 4, line 20, for "70" read 78 Signed and sealed this 7th day of April 1964.

(SEAL) Attest: EDWARD J. BRENNER ERNEST W. SWIDER Attesting Officer Commissioner of Patents 

1. A CONTINUOUS PROCESS FOR IMPROVING THE AESTHETICS OF A FABRIC CONTAINING A PREPONDERANCE OF FILAMENTS COMPOSED OF A SYNTHETIC, FIBER-FORMING POLYMER HAVING A MELT- 